The present invention relates in general to a method and apparatus for controlling an antenna signal combiner in a vehicle.
A primary source of noise and distortion in radio receivers is from multipath interference. This is a localized effect resulting from interaction between separate signals from a transmitter which traverse different paths (e.g., via reflections) to reach a receiving antenna. Because of the superposition of several signals (i.e., echoes and/or direct waves), the signal strength of the received signal changes drastically and may fall below the noise floor. Based upon the differences in path lengths of each received wave, the multipath distortion or fading may include short time delayed multipath interference and/or long-time delayed multipath interference signals. The multipath interference depends upon diverse geographic features and buildings. In an urban area with high buildings along both sides of a street, for example, the broadcast waves propagate along the street and become mixed with many short-time delayed signals. Along a riverside, long-time delayed signals may be mixed with both direct and quasi-direct signals. In a basin, there may be several long-time delayed signals arriving from different directions. This variability has made it difficult to solve the problem of multipath distortion in mobile radio receivers.
A well known means for reducing multipath distortion is through use of space-diversity antennas in a radio receiver system. By switching between antenna signals from spaced apart antennas, specific multipath events can be avoided if the antenna spacing is enough to insure that both antennas will not experience the same multipath event at the same time. However, since space diversity radio receiver systems cannot select only a single wave, they cannot completely avoid multipath distortion. The distortion is especially serious in long-time delay multipath conditions, such as may exist at a riverside or in a basin.
Another technique that has been used to reduce multipath interference is known as antenna beam steering. These systems use an antenna array which is operated in a manner to receive broadcast waves from a single direction only.
Beam steering systems have responded to changes in direction only indirectly by periodically sampling signals from various directions to find a beam steering direction which gives the best reception.
As the vehicle turns, beam steering systems will lose best reception momentarily as the system restores the beam direction to account for the vehicle change in direction. Tracking of the signal can be slow due to the response time of the system thereby causing poor reception.
The present invention has the advantage of providing a mobile receiver with greatly reduced multipath distortion while maintaining reasonable gain for the desired signal during reorientation (turning) of the vehicle.
In one aspect of the invention, a method is provided for controlling an antenna signal combiner in a vehicle having multiple antenna elements. The method includes receiving broadcast signals from the antenna elements. An antenna beam is then steered toward a first angle. Navigation data is then generated in response to a navigation sensor wherein the navigation data identifies a relative change in vehicle direction. Next, the antenna beam is steered toward a second angle in response to the relative change in vehicle direction.
Using changes in the heading of the vehicle with respect to antenna beam steering angle will allow better signal tracking, reduce distortion, and maintain a reasonable gain for the desired signal.